The invention relates to an electrical circuit for conveying information of the on/off type, in particular for use in the rail field.
In a train, numerous signals of the on/off type indicating the state of a parameter or of an item of equipment are conveyed, for example to an electronic circuit for controlling automatic logic controllers or to a monitoring and signalling panel. For example, such signals are representative of the state of a circuit-breaker or of the open or the closed position of a door giving access to a carriage, and they must be conveyed with a high degree of security and availability, which makes low-energy links of the computer type unsuitable for this type of use.
A solution that is currently used consists in connecting a closed-loop electrical circuit across the terminals of a storage battery, that circuit comprising, in series, at least one switch associated with the state of the member to be monitored, a resistor, and an isolated link connected to the device to which the information contained in the signal is addressed, e.g. the electronic circuit for controlling an automatic logic controller, or the monitoring and signalling panel.
The open or the closed position of the switch is representative of the state of a parameter or of an item of equipment. When the switch is closed, current whose magnitude is limited by the resistor, flows through the circuit. When it is open, no current flows. The presence or the absence of this current is transformed by the isolated link into on/off information communicated to the electronic circuit.
Generally, a train has a plurality of such circuits connected to the terminals of the same storage battery.
Since the switches tend to oxidize, some minimum current, of about a few tens of milliamps, must pass through each of the switches to clean them. The current is consumed and lost in the resistor. In addition, the power dissipated in the resistor by the Joule effect produces heat which must be removed. One known solution consists in using fans. However, currently the use of such fans as a mode of cooling the electronic circuits on board trains is avoided or even prohibited for reasons of reliability, since a fan includes mechanical components that might jam or seize and in general might fail.
Since the reliability of electrical and electronic components decreases greatly when the ambient temperature increases, it is desirable to produce as little heat as possible.
In addition, since the storage battery generally powers several circuits, and other items of equipment, the voltage that it delivers varies over time with varying load across its terminals. The current in the circuit thus also varies, in proportion to the charge of the storage battery.
As a result, to obtain the minimum current required for cleaning the switches, it must be accepted that a large amount of extra current and therefore power must be consumed during certain periods in the operation of the circuit. The resulting additional production of heat increases the problem of removing said heat.
The quantity of heat dissipated increases with the number of switches and of items of information to be transmitted.
The invention aims to reduce the above-mentioned drawbacks of the prior art.
An object of the invention is thus to convey an item of information of the on/off type with a high degree of reliability and availability, while reducing the power dissipated by the Joule effect.
To this end, the invention provides an electrical circuit for transmitting the state of a parameter or of an item of equipment, said electrical circuit being designed to be connected to the terminals of a power supply storage battery and comprising:
an isolated link between said electrical circuit and an output for transmitting an item of state information; and
a switch whose open position or whose closed position is representative of the state information and which determines whether current flows through said electrical circuit, the electrical circuit transmitting the state information from the switch to the output via the isolated link;
wherein, to regulate the magnitude of the current in the switch, said electrical circuit further comprises variable voltage generator means co-operating with switching means to power component elements of the electrical circuit selectively as a function of the output voltage of said variable voltage generator means, and wherein said electrical circuit further comprises inductive filter means in series with the switch, and capacitive storage means, each of which, under steady state conditions, forming energy-storage means and energy-yielding means for storing or yielding a portion of the energy of said electrical circuit, depending on the output voltage of the variable voltage generator.
According to other characteristics of the electrical circuit:
the inductive filter means are disposed in the immediate vicinity of the switch;
a diode is interposed between said switch and said inductive filter means, said diode being biased so as to prevent the current of the switch from flowing from the inductive filter means to the switch;
the inductive filter means are constituted by an inductor, the electrical circuit having, in series with the switch and the inductor, first and second branches in parallel, and having a resistor, in parallel with the switch and the inductor and connected to a point of the second branch, a capacitor being connected in the first branch, and the connection-switching means comprise a diode connected in the second branch between firstly one of the junctions of the first and second branches and secondly the point at which the resistance is connected to the second branch, the second branch further comprising a capacitor connected between firstly the other of the junctions of the first and second branches and secondly the point at which the resistor is connected to the second branch;
the isolated link is connected in series with the inductive filter means;
the isolated link is connected in series with the resistor;
the signal produced by the voltage generator means is a rectangular, triangular, or sinusoidal signal optionally centered on 0 volts;
the variable voltage generator means are connected in the first branch;
the isolated link consists of an optocoupler;
the isolated link consists of a transformer;
the isolated link consists of a transformer connected in series with the switch and whose primary also forms at least a portion of the inductive storage means; and
the switch is connected to a terminal of the storage battery, and a peak clipper is disposed between the output of said switch and the other terminal of the storage battery.
The invention also provides an electrical system designed to transmit a plurality of items of state information, said electrical system comprising a storage battery and a plurality of electrical circuits as defined above, each of which serves to transmit an item of state information, the circuits being connected in parallel to the terminals of the said storage battery.
According to another characteristic of the electrical system, it is on board a rail train, each switch being associated with a member or an item of equipment of said rail train, for monitoring the state or the position of said member or of said item of equipment.